NOVEL RECEPTOR-TYPE PHOSPHOTYROSINE PHOSPHATASE-BETA

Abstract: A novel receptor-type protein tyrosine phosphatase- beta (RPTP beta ) protein or glycoprotein, and the DNA coding therefor is disclosed. This protein is naturally expressed in the brain and in neural cell lines. The RPTP beta protein or glycoprotein may be produced by recombinant means. Antibodies to the protein, methods for measuring the quantity of the protein, methods for screening compounds, such as drugs, which can bind to the protein and inhibit or stimulate its phosphatase enzymatic activity, are provided.

Description: NOVEL RECEPTOR-TYPE PHOSPHOTYROSINE PHOSPHATASE-BETA The present application is a continuation-in-part of U.S application Serial No. 07/654,188, filed February 26, 1991, which was a continuation-in-part of U.S. application Serial No. 07/551,270, filed July 11, 1990, now abandoned. The entire contents of both of the above applications are hereby incorporated by reference. 1. INTRODUCTION The invention in the field of biochemistry and cell and molecular biology relates to novel receptor- type protein tyrosine phosphatase proteins or glycoproteins, termed RPTPα, β and 7, DNA coding therefor, methods for production and identification of the proteins, and methods for screening compounds capable of binding to and inhibiting or stimulating PTPase enzymatic activity. 2. BACKGROUND OF THE INVENTION The identification of several growth factor receptors and retroviral oncogenes as tyrosine- specific protein kinases indicated that protein phosphorylation on tyrosine residues plays a key role in cellular growth control. This notion has recently received support by the observation that the level of tyrosine phosphorylation of enzymes thought to play an important role in signal transduction (such as phospholipase C) correlates with their increased activity upon growth factor stimulation, thus establishing a functional role for tyrosine phosphorylation (Ullrich, A., et al.. Cell 61:203-212 (1990) ) . The degree and pattern of phosphorylation of tyrosine residues on cellular proteins are regulated by the opposing activities of protein-tyrosine kinases (PTKases; ATP:protein-tyrosine O-phosphotransferase, EC 2.7.1.112) and protein-tyrosine-phosphatases (PTPases; protein-tyrosine-phosphate phosphohydrolase, EC 3.1.3.48). The structural characteristics and evolution of PTKases as well as their role in the regulation of cell growth have been reviewed (Hunter, T. , et al.. Annu. Rev. Biochem. 5_4:897-930 (1985); Ullrich, A. , et al. , supra ) . 2.1. PTKases Tyrosine kinases comprise a discrete family of enzymes having common ancestry with, but major differences from, serine/threonine-specific protein kinases (Hanks, S.K. et al.. (1988) Science 241, 42- 52) . The mechanisms leading to changes in activity of tyrosine kinases are best understood for receptor-type tyrosine kinases which have a transmembrane topology (Ullrich, A. et al.. supra.. V7ith such kinases, the binding of specific ligands to the extracellular domain of these enzymes is thought to induce their oligomerization leading to an increase in tyrosine kinase activity and activation of the signal transduction pathways (Ullrich, A. et al.. supra) . The importance of this activity is supported by the knowledge that dysregulation of kinase activity through mutation or over-expression is a mechanism for oncogenic transformation (Hunter, T et al. , supra; Ullrich, A. et al.. 1990, supra) . 2 . 2 . PTPases The protein phosphatases are composed of at least two separate and distinct families (Hunter, T. Cell. 58.:1013-1016 (1989)), the protein serine/threonine phosphatases and the protein tyrosine phosphatases. This is in contrast to protein kinases, which show clear sequence similarity between serine/threonine- specific and tyrosine-specific enzymes. There appear to be two varieties of PTPase molecules. The first group is comprised of small, soluble enzymes that contain a single conserved phosphatase catalytic domain, and include (1) placental PTPase IB (Charbonneau, H. et al. , Proc. Natl. Acad. Sci. 86:5252-5256 (1989); Chemoff, J. et al.. Proc. Natl. Acad. Sci. USA 87:2735-2789 (1990)), (2) T-cell PTPase (Cool, D.E. et al.. Proc. Natl. Acad. Sci. USA 86:5257- 5261 (1989)), and (3) rat brain PTPase (Guan, K. , et al.. Proc. Natl. Acad. Sci. USA. £7:1501- 1505 (1990). The second group is made up of the more complex, receptor-linked PTPases, termed RPTPs, which are of high molecular weight and contain two tandemly repeated conserved domains separated by 56-57 amino acids. One example of RPTPs are the leukocyte common antigens (LCA) (Ralph, S.J., EMBO J.. 6:1251-1257 (1987); Charbonneau, H. , et al. , Proc. Natl. Acad. Sci. USA. 5:7182-7186 (1988)). LCA, also known as CD45, T200 and Ly-5 (reviewed in Thomas, M.L., Ann. Rev. Immunol. 2:339-369 (1989)) comprises a group of membrane glycoproteins expressed exclusively in hemopoietic (except late erythroid) cells, derived from a common gene by alternative splicing events involving the amino terminus of the proteins. Whereas the precise function of CD45 is unknown, many studies have implicated these antigens in a number of processes, including the activity of cytotoxic T lymphocytes and natural killer cells, IL-2 receptor expression, B-cell differentiation, and T lymphocyte proliferation (Pingel, J.T. et al.. Cell 58:1055-1065 (1989)) . Other examples of RPTPs are the LCA-related protein, LAR (Streuli, M. , et al.. J. Exp. Med.. 168:1523-1530 (1988)), and the LAR-related Drosophila proteins DLAR and DPTP (Streuli, M. , et al. , Proc. Natl. Acad. Sci. USA. £6:8698-8702 (1989)). Jirik et al. screened a cDNA library derived from the human hepatoblastoma cell line, HepG2, with a probe encoding the two PTPase domains of LCA (FASEB J. 4 . :A2082 (1990), abstr. 2253) and discovered a cDNA clone encoding a new RPTP, named He-PTP. The HePTP gene appeared to be expressed in a variety of human and murine cell lines and tissues. While we are beginning to understand more about the structure and diversity of the PTPases, much remains to be learned about their cellular functions. It has been suggested (Tonks, N.K., et al.. Biochemistry. 22:8695-8701 (1988)) that the small, soluble PTPase enzymes may have a "housekeeping" function. On the other hand, the RPTPs would be expected to be more restricted in their activities because of their location in the cell membrane and their potential regulation by extracellular ligands. Regarding the role of LCA (CD45) in T cells, it was found that T cell clones deficient in the expression of LCA failed to proliferate when stimulated by a specific antigen or by cross-linking of CD3 (Pingel, J.T., et al.. supra) . PTPase cross-linking inhibits T cell receptor CD3-mediated activation in human T cells (Kiener, P.A. et al.. J. Immunol. 143:23-28 (1989)). The PTPase activity of LCA plays a role in the activation of pp56 k , a lymphocyte-specific PTKase (Mustelin, T. , et al.. Proc. Natl. Acad. Sci. USA. £6_:6302-6306 (1989) ; Ostergaard, H.L. , et al.. Proc. Natl. Acad. Sci. USA. £6_:8959-8963 (1989)) . These authors hypothesized that the phosphatase activity of LCA activates pp56 k * by dephosphorylation of a C- terminal tyrosine residue, which may, in turn, be related to T-cell activation. Using site-directed mutagenesis to determine which of four conserved cysteines in LCA (two per phosphatase domain) was required for enzyme activity toward artificial substrates, Streuli et al. (1989, supra) found that only one cysteine residue (residue 177 of LCA phosphatase domain-1) of LCA was essential for activity, indicating that, most likely, only the first phosphatase domain has enzymatic activity. However, the possibility that the second domain can dephosphorylate a different substrate was not excluded. More recently, Streuli et. al. (EMBO J.. 9_:2399-2407 (1990)) determined that the second conserved domain of LCA (and of LAR) lacked detectable phosphatase activity but sequences within the domain could influence substrate specificity. In order to better understand and to be able to control phosphotyrosine metabolism, one must comprehend not only the role of kinase activity, but also the action of phosphatase enzymes as well. Elevation of cellular phosphotyrosine may occur through mechanisms not involving the activation of a tyrosine kinase itself. For instance, expression of the v-crk oncogene, though not a tyrosine kinase itself, induces the phosphorylation of tyrosine residues through a poorly understood mechanism (Mayer, B.J. et al. (1988) Nature 332, 272-275) . Potentially, such an outcome could result from either mutation of the substrate or through a general decrease in cellular phosphatase activity, especially in view of the normally high turnover rate of cellular tyrosine- phosphate (Sefton, B.M. et al. (1980) Cell 20, 807- 816) . The latter possibility is suggested by the demonstration that tyrosine phosphatase inhibitors can "reversibly transform" cells (Klarlund, J.K. Cell 41: 707-717 (1985)). PTPases could therefore be viewed as potential recessive oncogenes. It is becoming clear that dephosphorylation of tyrosine can by itself function as an important regulatory mechanism. Dephosphorylation of a C- terminal tyrosine residue stimulates tyrosine kinase activity in the src-family of tyrosine kinases (Hunter, T. (1987) Cell 49, 1-4). Tyrosine dephosphorylation has been suggested to be an obligatory step in the mitotic activation of the MPF (maturation promoting factor) kinase (Morla, A.O. et al. (1989) Cell 58, 193-203). Lastly, mutant analysis of primitive eukaryotes has established crucial roles for serine phosphatase in cellular physiology (Cyert, M.S. et al. (1989) Cell 57, 891-893). These observations point out the need in the art for increasing our understanding of the mechanisms that regulate tyrosine phosphatase activity. It is clear in the art that further analysis of structure-function relationships among these membrane receptors are needed to gain important understanding of the mechanisms of cell growth, differentiation, and oncogenesis. 3. SUMMARY OF THE INVENTION The present inventor has conceived of a role for RPTPs in cellular control mechanisms, both as potential anti-oncogenes, and as effectors in a newly discovered mechanism of transmembrane signalling. They therefore undertook a search for individual RPTP genes and proteins potentially involved in such processes, and describe herein the identification of a novel, member of the RPTP family, RPTP3, which has a transmembrane topology. The extracellular domains of members of this RPTP family are unrelated to any other RPTPs previously described. The novel RPTP/3, in a manner analogous to receptor tyrosine kinases, is subject to direct regulation by extracellular ligands which bind to the extracellular portion. The present invention thus provides a human receptor-type protein tyrosine phosphatase-/-? (RPTP/3) protein or glycoprotein molecule, a functional derivative of the human RPTP/3 or a homolog of human RPTP/3 in another mammalian species. When the RPTP3 molecule is of natural origin, it is substantially free of other proteins or glycoproteins with which it is natively associated. RPTP/3 is naturally expressed in mammalian brain and is developmentally and anatomically regulated. The RPTP/3 molecule of the present invention may not be of natural origin, and, may be prepared by chemical or recombinant means. Thus, the substantially pure RPTP/3 protein or glycoprotein of the present invention may be produced by biochemical purification of the protein or glycoprotein of natural origin; alternatively, the RPTP3 may be produced by recombinant means in prokaryotic or eukaryotic hosts. In particular, the invention is directed to a RPTP3 having the amino acid sequence SEQ ID NO:l of human RPTPβ, shown in Figures 1 and>2, or a functional derivative thereof. The invention is further directed to a nucleic acid molecule, preferably, DNA, consisting essentially of a nucleotide sequence encoding RPTPβ, preferably of human origin, or encoding a functional derivative thereof. The nucleic acid molecule, preferably comprises the sequence SEQ ID NO:2 (see Figure 1). The DNA molecule is preferably cDNA or genomic DNA. The invention is further directed to the DNA molecule in the form of an expression vehicle, as well as prokaryotic and eukaryotic hosts transformed or transfected with the DNA molecule. Also included in the present invention is a process for preparing an RPTP/3 protein or glycoprotein, or a functional derivative thereof, comprising: (a) culturing a host capable of expressing the protein, glycoprotein or functional derivative under culturing conditions; (b) expressing the protein, glycoprotein or functional derivative; and (c) recovering the protein, glycoprotein or functional derivative from the culture. The invention is directed to an antibody, either polyclonal, monoclonal, or chimeric, which is specific for the RPTP3 protein or glycoprotein. The invention is also directed to a method for detecting the presence of nucleic acid encoding a normal or mutant RPTP/3 in a subject comprising: (a) contacting a cell or an extract thereof from the subject with an oligonucleotide probe encoding at least a portion of the normal or mutant RPTP/3 under hybridizing conditions; and (b) measuring the hybridization of the probe to the nucleic acid of the cell, thereby detecting the presence of the nucleic acid. The DNA can be selectively amplified, using the polymerase chain reaction, prior to assay. The invention is further directed to a method for detecting the presence, or measuring the quantity of RPTP3 in a cell or cells, comprising: (a) contacting said cell or an extract thereof with an antibody specific for an epitope of the RPTP3; and (b) detecting the binding of the antibody to the cell or extract thereof, or measuring the quantity of antibody bound, thereby detecting the presence or measuring the quantity of the RPTPβ. Tne present invention is also directed to methods for identifying and isolating a compound capable of binding to RPTPβ from a chemical or biological preparation comprising: (a) attaching the RPTP/3, or the ligand-binding portion thereof, to a solid phase matrix; (b) contacting the chemical or biological preparation with the solid phase matrix allowing the compound to bind, and washing away any unbound material; (c) detecting the presence of the compound bound to the solid phase; and, for purposes of isolation, (d) eluting the bound compound, thereby isolating the compound. Finally, the invention includes a method for identifying an agent capable of stimulating or inhibiting the phosphatase enzymatic activity of RPTP/3, comprising: - io ¬ ta) contacting the agent with RPTP/3 in pure form, in a membrane preparation, or in a whole live or fixed cell; (b) incubating the mixture in step (a) for a sufficient interval; (c) measuring the enzymatic activity of RPTP3; (d) comparing the enzymatic activity to that of RPTP/S incubated without the agent, thereby determining whether the agent stimulates or inhibits the activity. 4. DESCRIPTION OF THE FIGURES Figure 1 shows the nucleotide sequence (SEQ ID NO:2) and predicted amino acid sequence (SEQ ID NO:l) of human RPTP3. Figure 2 presents the amino acid sequence of RPTP3. The hydrophobic signal peptide is underlined and the transmembrane peptide is designated in bold. The 21 potential N-glycosylation sites are indicated by filled arrows. The CAH-related domain and the two phosphatase domains, DI and DII, are indicated by the boxes. The open arrows represent the boundaries of the deletion in the variant RFTPβ clones. Figure 3 describes the identification of a CAH- related domain in the extracellular region of RPTP/3. Figure 3A shows an alignment of the amino acid sequence of the CAH-related domain of RPTPjS with the corresponding domain of RPTPγ and six different isoforms of CAH (I-VII) . The amino acid sequences that are boxed in black are those that are identical in all six isoforms of CAH. The sequences boxed in the gray hatches are those that are identical between the CAH-related domains of RPTPβ and RPTP7. Figure 3B is a table showing the percent similarity (taking into account conservative amino acid substitutions) between the CAH-related domains of RPTP/3, RPTP7 and the six isoforms of CAH. Figure 4 shows the chromosomal localization of human RPTP/3. A completely stippled box indicates that the hybrid designated in the left column contains the chromosome indicated in the upper row; lower-right stippling indicates the presence of the long arm (or a part of the long arm, indicated by small fraction of stippling) of the chromosome indicated; upper left stippling indicates the presence of the short arm (or partial short arm) of the chromosome indicated; an open box indicates absence of the chromosome indicated; the column for chromosome 7 is boldly outlined and stippled to highlight the correlation of the presence of this chromosome with the presence of the RPTP/3 gene. The pattern of retention of the RPTPβ sequences in the hybrids is shown on the right where the presence of the gene is indicated by a "+" sign in a stippled box and absence of the gene is indicated by a "-" sign in an open box. Figure 4B shows a schematic diagram of chromosome 7, indicating that RPTP/3 maps to 7q31-q33. chromosomal in situ hybridization of a 1.8 kb RPTP/3 cDNA to normal human metaphase chromosomes confirmed localization of the gene to 7q and revealed a peak of grains centered over the 7q31.3-q32 region, as illust4rated. Each dot to the right represents an autoradiographic grain. Figure 5 shows the expression of RPTP3 m NA in various human cell lines and murine tissues using Northern blot analysis. In Figure 5A, 20 μg of total cellular RNA (lanes 1-5) or 1 μg of poly-A + RNA (lane 6) isolated from the various indicated glioblastoma and neuroblastoma cell lines were loaded onto a 1% agarose/2.2M formaldehyde RNA gel and probed with a DNA fragment isolated from the human brain stem cDNA clone that begins with sequences just 5' of the region encoding the transmembrane region and extends and includes all of the sequence in the phosphatase domain I. In Figure 5B, poly-A + RNA (1 μg/sample) from the indicated murine tissues were loaded onto an RNA gel and probed with the PCR-amplified murine DNA fragment, pBSMBDII. Figure 5C shows the blot from Figure 5B which was stripped of the probe and rehybridized with a 32 P-labeled rat actin probe. Figure 6 is a gel pattern showing the identification of endogenous RPTP3 protein expressed in Lan 5 cells. RPTP/3 was immunoprecipitated with normal rabbit serum (NRS, lane 1) or immune anti-RPTP3 antiserum (αPTP/3, lanes 2 and 3) from lysates of [ 35 S]methionine-labeled Lan 5 cells in the absence (lanes 1 and 2) or presence (lane 3) of tunicamyσin. Immunoprecipitation of the EGF receptor with RK2 antibody (αEGFR, lanes 4 and 5) from lysates of [ 35 S]methionine-labeled Lan 5 cells labeled in the absence (lane 4) or presence (lane 5) of tunicamycin. Figure 7 (Fig. 6) shows the identification of variant RPTP3 using Northern blots. Figure 7A is a schematic diagram of the protein encoded by the full length RPTP/3 cDNA compared to the putative protein encoded by the two independently isolated cDNA clones that carry an identical deletion of 2577 bp in the extracellular region of the protein. The position of the deletion is indicated by the dotted line with the number of amino acids remaining at both the 5' and 3' end of the deletion indicated. The location of the two probes using in Northern analysis (probes 1 and 2) are indicated. TM, transmembrane peptide; DI, phosphatase domain I; DII, phosphatase domain II. Figure 7B shows the results of Northern analysis. poly-A + RNA (1 μg) isolated from the Lan 5 neuroblastoma cell line was separated on a RNA formaldehyde gel and probed with human probe 1 (Pl) that contains 1.3 kb of sequences derived from the extreme 5' end of the cDNA clone and human probe 29P2) that contains 1.6 kb of sequences derived from the portion of the full length cDNA clone that is deleted in the variant cDNA clones. Figure 8 shows the results of an in situ hybridization analysis of RPTP/3 expression in developing and adult mouse brain. Figure 8A shows a sagittal section through an embryonic day 20 (E2) mouse, and indicates that RPTP/3 was expressed in the developing nervous system. The highest level of expression was observed in the ventricular and subventricular zones (VZ) . Figure 8B is a sagittal section through an adult mouse brain and shows discrete bands of expression in the Purkinje cells of the cerebellum (PK) , the dentate gyrus (DG) , and the subependymal layer of the anterior horn of the lateral ventricle (AH) . 5. DETAILED DESCRIPTION OF THE INVENTION Through the use of recombinant DNA methods, the present inventor has identified novel mammalian receptor-type (transmembrane) protein tyrosine phosphatases (PTPase; EC 3.1.3.48) . In view of their receptor-like structure, and the likelihood that they are part of a family, the inventor has termed these protein, RPTPα, RPTP/3, RPTP7, etc. (receptor protein tyrosine phosphatase-alpha, beta, gamma, etc.). The family is designated herein as the "RPTPs" (and is also referred to as R-PTPases) Human RPTP3 is a protein or glycoprotein having 2307 amino acids. In contrast, human RPTPα has 802 amino acids and human RPTP7 has 1445 amino acids. RPTP/3 has an extracellular domain, a single transmembrane domain and a cytoplasmic portion with two tandem catalytic phosphatase domains. The extracellular domain contains a stretch of 266 amino acids with striking ho ology to the zinc-containing enzyme carbonic anhydrase (CAH) indicating that RPTP3 together with RPTP7 (HPTPf) represent a subfamily of RPTPs. The gene encoding RPTP/3, denoted RJP Pβ (or PTPξ) has been mapped by the present inventor to human chromosome 7 q 31- 33, a site rather distinct from the site to which RPTP7 was mapped (3 p 14.2- p 21) . The cDNA cloning of human RPTP/3, and the complete DNA and amino acid sequence of human RPTP/J are described herein. Northern analysis has been used to identify the natural expression of the protein in various cells and tissues. RPTP7 was shown to be expressed in anatomically distinct regions of rat brain and its expression was found to be developmentally regulated. Remarkably, in addition to being composed of intracellular domains having enzymatic activity, the receptor family to which RPTPs belong includes transmembrane proteins having and N-terminal extracellular domains, analogous to the tyrosine kinase enzyme family (Tonks, N.K. et al . (1988) Biochemistry 27:8695-8701; Charbonneau, H. et al . (1988) Proc . Natl . Acad . Sci . USA 85:7182-7186; Streuli, M. et al. (1988) J . Exp . Med . 168:1523- 2530; Streuli, M. et al . (1989) Proc. Natl . Acad . Sci . USA 86:8698-8702). The present inventor has therefore concluded that ligands in the extracellular environment can control the activity of this membrane- associated subclass of PTPases. The present inventor has further produced a polyclonal antibody to RPTPβ by immunization or rabbits with a 15 amino acid synthetic peptide of RPTPjS conjugated to a carrier. RPTP/3 is useful in methods for screening drugs and other agents which are capable of activating or inhibiting the PTPase enzymatic activity, and thereby affecting major pathways of cellular metabolism. By attaching an intact RPTPβ, or the ligand-binding portion thereof, to a solid phase matrix, an affinity probe is created which can be used to screen biological products or chemical agents for their capacity to interact with the receptor on the basis of their binding activity. Bound material can then be eluted from the affinity probe in purified form. Methods for coupling proteins and peptides to the solid phase, the solid phase substances useful in these methods, and means for elution, are well known to those of skill in the art. The RPTPjS protein or derivatives thereof having enzymatic activity can be used for testing of compounds capable of enhancing or inhibiting the phosphatase activity. The ability of a compound under test to modify phosphatase activity can be tested in an in vitro system wherein the test compound is added to purified RPTP/3 protein, or an enzymatically active derivative thereof, and the affects on enzyme activity measured using standard enzymological procedures well known to those of skill in the art. Alternatively, the action of a compound on RPTP/3 enzymatic activity can be measured in a whole cell preparation using live or fixed cells, or a membrane fraction derived from live or fixed cells. This method is useful for screening compounds acting via the extracellular receptor portion of the protein, as well as compounds acting directly on the enzymatic portion of the protein. A test compound is incubated with cells, or with a membrane preparation derived therefrom, which express high amounts of the RPTP / 3, such as transfected COS or NIH-3T3 cells. The amount of cellular phosphotyrosine is then measured, using methods well-known in the art (Honegger, A.M. et al.. Cell 51:199-209 (1987); Margolis, B. et al.. Cell 52:1101-1107 (1989)). The results are compared to results obtained in the absence of the test compound, or in the absence or presence of a known activator of RPTP0 enzymatic. In such studies, the action of the test compound in the presence of an activator of tyrosine kinase can also be measured. A compound which stimulates RPTP3 enzymatic activity will result in a net decrease in the amount of phosphotyrosine, whereas a compound which inhibits RPTP/3 enzymatic activity will result in a net increase in the amount of phosphotyrosine. In the case of growth factor receptors which are tyrosine kinases, such as the receptors for epidermal growth factor (EGF) and for platelet-derived growth factor (PDGF) , tyrosine phosphorylation is linked to cell growth and to oncogenic transformation. Activation of a PTPase, leading to dephosphorylation, would serve as a counterregulatory mechanism to prevent or inhibit growth, and might serve as an endogenous regulatory mechanism against cancer. Thus, mutation or dysregulation of this receptor/enzyme system may promote susceptibility to cancer The insulin receptor is also a tyrosine kinase, and phosphorylation of tyrosine in cells bearing insulin receptors would be associated with normal physiological function. In contrast to the case of cell growth and cancer, activation of an RPTP would counteract insulin effects. Subnormal RPTP levels or enzymatic activity would act to remove a normal counterregulatory mechanisms. Perhaps more important, though, over-activity, or inappropriate activation, of an RPTP such as RPTPS would be expected to partially or totally inhibit the action of insulin on cells, leading to diabetes (of an insulin-resistant variety) . Thus, susceptibility to diabetes may be associated with RPTPjβ dysregulation. Therefore, the methods of the present invention for identifying normal or mutant RPTP/3 genes, or for measuring the amount or activity of RPTP/3 associated with a cell or tissue, can serve as methods for identifying susceptibility to cancer, diabetes, or other diseases associated with alterations in cellular phosphotyrosine metabolism. The present invention provides methods for evaluating the presence of, and the level of, normal or mutant RPTP/3 in a cell or in a subject. Absence, or more typically, low expression of RPTP/3, or presence of a mutant RPTP/3, in an individual may serve as an important predictor of susceptibility to oncogenic transformation and the development of cancer. Alternatively, over-expression of RPTP3, possibly due to a mutant receptor/enzyme system insensitive to negative regulation, or due to overabundance of a stimulatory ligand in the body, may serve as an important predictor of susceptibility to diabetes. An oligonucleotide probe encoding a part of the RPTPjS sequence (see below) is used to test cells from a subject for the presence DNA or RNA sequences encoding the RPTP/3. A preferred probe would be one directed to the nucleic acid sequence encoding at least 4 amino acid residues, and preferably at least 5 amino acid residues, of the RPTP/3. Qualitative or quantitative assays can be performed using such probes. For example, Northern analysis (see Sections 8 and 10 below) is used to measure expression of an RPTP/3 mRNA in a cell or tissue preparation. Such methods can be used even with very small amounts of DNA obtained from an individual, following use of selective amplification techniques. Recombinant DNA methodologies capable of amplifying purified nucleic acid fragments have long been recognized. Typically, such methodologies involve the introduction of the nucleic acid fragment into a DNA or RNA vector, the clonal amplification of the vector, and the recovery of the amplified nucleic acid fragment. Examples of such methodologies are provided b Y Cohen et al. (U.S. Patent 4,237,224), Sambrook et al. Molecular Cloning: A Laboratory Manual. Second Edition, Cold Spring Harbor Press, Cold Spring Harbor, NY (1989) , which references are herein incorporated by reference) . An in vitro, enzymatic method which is capable of increasing the concentration of such desired nucleic acid molecules is called the "polymerase chain reaction or "PCR" (Mullis, K. et al.. Cold Soring Harbor Svmp. Quant. Biol. 51:263-273 (1986); Erlich, H. et al.. EP 50,424; EP 84,796, EP 258,017, EP 237,362; Mullis, K. , EP 201,184; Mullis, K. et al.. US 4,683,202; Erlich, H., US 4,582,788; and Saiki, R. et al.. US 4,683,194) . The PCR provides a method for selectively increasing the concentration of a particular nucleic acid sequence even when that sequence has not been previously purified and is present only in a single copy in a particular sample. The method can be used to amplify either single- or double-stranded DNA. The essence of the method involves the use of two oligonucleotide probes to serve as primers for the template-dependent, polymerase mediated replication of a desired nucleic acid molecule. The precise nature of the two oligonucleotide probes of the PCR method is critical to the success of the method. Polymerase dependent amplification of a nucleic acid molecule proceeds by the addition of a 5' nucleotide triphosphate to the 3 • hydroxyl end of a nucleic acid molecule. Thus, the action of a polymerase extends the 3 * end of a nucleic acid molecule. These inherent properties are exploited in the selection of the oligonucleotide probes of the PCR. The oligonucleotide sequences of the probes of the PCR method are selected such that they contain sequences identical to, or complementary to, sequences which flank the particular nucleic acid sequence whose amplification is desired. More specifically, the oligonucleotide sequences of the "first" probe is selected such that it is capable of hybridizing to an oligonucleotide sequence located 3 • to the desired se¬ quence, whereas the oligonucleotide sequence of the "second" probe is selected such that it contains an oligonucleotide sequence identical to one present 5' to the desired region. Both probes possess 3' hydroxy groups, and therefore can serve as primers for nucleic acid synthesis. PCR reaction conditions are cycled between (a) those conducive to hybridization and nucleic acid polymerization, and (b) those which result in the denaturation of duplex molecules. In the first step of the reaction, the nucleic acids of the sample are transiently heated, and then cooled, in order to denature any double-stranded molecules which may be present. The "first" and "second" probes are then added to the sample at a concentration which greatly exceeds that of the desired nucleic acid molecule. When the sample is incubated under conditions conducive to hybridization and polymerization, the "first" probe will hybridize to the nucleic acid molecule of the sample at a position 3• to the sequence to be amplified. If the nucleic acid molecule of the sample was initially double-stranded, the "second" probe will hybridize to the complementary strand of the nucleic acid molecule at a position 3' to the sequence which is the complement of the sequence whose amplification is desired. Upon addition of a polymerase, the 3* ends of the "first" and (if the nucleic acid molecule was double-stranded) "second" probes will be extended. The extension of the "first" probe will result in the synthesis of an oligonucleotide having the exact sequence of the desired nucleic acid. Extension of the "second" probe will result in the synthesis of an oligonucleotide having the exact sequence of the complement of the desired nucleic acid. The PCR reaction is capable of exponential amplification of specific nucleic acid sequences because the extension product of the "first" probe, of necessity, contains a sequence which is complementary to a sequence of the "second" probe, and thus can serve as a template for the production of an extension product of the "second" probe. Similarly, the extension product of the "second" probe, of necessity, contains a sequence which is complementary to a sequence of the "first" probe, and thus can serve as a template for the production of an extension product of the "first" probe. Thus, by permitting cycles of polymerization, and denaturation, a geometric increase in the concentration of the desired nucleic acid molecule can be achieved. Reviews of the PCR are provided by Mullis, K.B. (Cold Spring Harbor Symp. Quant. Biol. 51:263-273 (1986)); Saiki, R.K. , et al. (Bio/Technology 3:1008-1012 (1985)); and Mullis, K.B., et al. tMeth . Enzvmol. 155:335-350 (1987)). In one embodiment, the present invention is directed to a naturally occurring mammalian RPTP/3. In another embodiment, the invention is directed to a recombinant mammalian RPTPβ. The preferred mammalian RPTPjS of the present invention is of human origin. The invention provides the naturally occurring molecule substantially free of other proteins with which it is natively associated. "Substantially free of other proteins or glycoproteins" indicates that the protein has been purified away from at least 90 per cent (on a weight basis) , and from even at least 99 per cent if desired, of other proteins and glycoproteins with which it is natively associated, and is therefore substantially free of them. That can be achieved by subjecting the cells, tissue or fluid containing the RPTPβ to standard protein purification techniques such as immunoabsorbent columns bearing an antibody specific for the protein. Other forms of affinity purification can utilize solid-phase substrates which can bind the PTPase domain, or a ligand that will bind to the receptor domain. Alternatively, the purification can be achieved by a combination of standard methods, such as ammonium sulfate precipitation, molecular sieve chromatography, and ion exchange chromatography. It will be understood that the RPTP/3 of the present invention can be biochemically purified from a variety of cell or tissue sources. For preparation of naturally occurring RPTP / 3, tissues such as mammalian brain, especially of human origin, are preferred. Alternatively, because the gene for the RPTP3 can be isolated or synthesized, the polypeptide can be synthesized substantially free of other proteins or glycoproteins of mammalian origin in a prokaryotic organism or in a non-mammalian eukaryotic organism, if desired. As intended by the present invention, a recombinant RPTP/3 molecule produced in mammalian cells, such as transfected COS, NIH-3T3, or CHO cells, for example, is a protein with a naturally occurring amino acid sequence or is a functional derivative thereof. Where a naturally occurring protein or glycoprotein is produced by recombinant means, it is provided substantially free of the other proteins and glycoproteins with which it is natively associated. Alternatively, methods are well known for the synthesis of polypeptides of desired sequence on solid phase supports and their subsequent separation from the support. In a further embodiment, the invention provides "functional derivatives" of the RPTPβ. By "functional derivative" is meant a "fragment," "variant," "analog," or "chemical derivative" of RPTP/3, which terms are defined below. A function al derivative retains at least a portion of the function of the RPTPβ, such as (a) binding to a specific antibody, (b) phosphatase enzymatic activity or (c) binding of the extracellular "receptor" domain to a ligand, which permits its utility in accordance with the present invention. A "fragment" of the RPTP/3 refers to any subset of the molecule, that is, a shorter peptide. A "variant" of the RPTP0 refers to a molecule substantially similar to either the entire peptide or a fragment thereof. Variant peptides may be conveniently prepared by direct chemical synthesis of the variant peptide, using methods well- known in the art. Alternatively, amino acid sequence variants of the peptide can be prepared by mutations in the DNA which encodes the synthesized peptide. Such variants include, for example, deletions from, or insertions or substitutions of, residues within the amino acid sequence. Any combination of deletion, insertion, and substitution may also be made to arrive at the final construct, provided that the final construct possesses the desired activity. Obviously, the mutations that will be made in the DNA encoding the variant peptide must not alter the reading frame and preferably will not create complementary regions that could produce secondary mRNA structure (see European Patent Publication No. EP 75,444). At the genetic level, these variants ordinarily are prepared by site-directed mutagenesis (as exemplified by Adel an et al. , DNA 2:183 (1983)) of nucleotides in the DNA encoding the peptide molecule, thereby producing DNA encoding the variant, and thereafter expressing the DNA in recombinant cell culture. The variants typically exhibit the same qualitative biological activity as the nonvariant peptide. An "analog" of the RPTP/3 refers to a non-natural molecule substantially similar to either the entire molecule or a fragment thereof. A "chemical derivative" of the RPTP3 contains additional chemical moieties not normally a part of the peptide. Covalent modifications of the peptide are included within the scope of this invention. Such modifications may be introduced into the molecule by reacting targeted amino acid residues of the peptide with an organic derivatizing agent that is capable of reacting with selected side chains or terminal residues. Cysteinyl residues most commonly are reacted with alpha-haloacetates (and corresponding amines) , such as chloroacetic acid or chloroacetamide, to give carboxymethyl or carboxyamidomethyl derivatives. Cysteinyl residues also are derivatized by reaction with bromotrifluoroacetone, α-bromo-/3-(5- imidozoyl)propionic acid, chloroacetyl phosphate, N- alkylmaleimides, 3-nitro-2-pyridyl disulfide, methyl 2-pyridyl disulfide, p-chloromercuribenzoate, 2- chloromercuri-4- nitrophenol, or chloro-7-nitrobenzo- 2-oxa-l,3-diazole. Histidyl residues are derivatized by reaction with diethylprocarbonate, pH 5.5-7.0, because this agent is relatively specific for the histidyl side chain. Para-brcmophenacyl bromide also is useful; the reaction is preferably performed in 0.1 M sodium cacodylate at pH 6.0. Lysinyl and amino terminal residues are reacted with succinic or other carboxylic acid anhydrides. Derivatization with these agents has the effect of reversing the charge of the lysinyl residues. Other suitable reagents for derivatizing α-amino-containing residues include imidoesterε such as methyl picolinimidate; pyridoxal phosphate; pyridoxal; chloroborohydride; trinitrobenzenesulfonic acid; O- methylisourea; 2,4 pentanedione; and transaminaεe- catalyzed reaction with glyoxylate. Arginyl residues are modified by reaction with one or several conventional reagents, among them phenylglyoxal, 2,3- butanedione, 1,2-cyclohexanedione, and ninhydrin. Derivatization of arginine residues requires that the reaction be performed in alkaline conditions because of the high pK a of the guanidine functional group. Furthermore, these reagents may react with the groups of lysine as well as the arginine e-amino group. The specific modification of tyrosyl residues per --i-t nas bee studied extensively, with particular interest in introducing spectral labels into tyrosyl residues by reaction with aromatic diazonium compounds or tetranitromethane. Most commonly, N-acetylimidizol and tetranitromethane are used to form O-acetyl tyrosyl species and 3-nitro derivatives, respectively. Carboxy1 side groups (aspartyl or glutamyl) are selectively modified by reaction with carbodiimides (R'-N-C-N-R') such as l-cyclohexyl-3-(2-morpholinyl- (4-ethyl) carbodiimide or l-ethyl-3-(4-azonia-4,4- dimethylpentyl) carbodiimide. Furthermore, aspartyl and glutamyl residues are converted to asparaginyl and glutaminyl residues by reaction with ammonium ions. Glutaminyl and asparaginyl residues may be deamidated to the corresponding glutamyl and aspartyl residues, under mildly acidic conditions. Either form of these residues falls within the scope of this invention. Derivatization with bifunctional agents is useful for cross-linking the protein or peptide to a water- insoluble support matrix or to other macromolecular carriers. Commonly used cross-linking agents include, e.g. , 1,l-bis(diazoacetyl)-2-phenylethane, glutaraldehyde, N-hydroxysuccinimide esters, for example, esters with 4-azidosalicylic acid, homobifunctional imidoesters, including disuccinimidyl esters such as 3,3'- dithiobis(succinimidyl- propionate) , and bifunctional maleimides such as bis- N-maleimido-1,8-octane. Derivatizing agents such as methyl-3-[ (p-azidophenyl)dithio]propioimidate yield photoactivatable intermediates that are capable of forming crosslinks in the presence of light. Alternatively, reactive water-insoluble matrices such as cyanogen bromide-activated carbohydrates and the reactive substrates described in U.S. Patent Nos. 3,969,287; 3,691,016; 4,195,128; 4,247,642; 4,229,537; and 4,330,440 are employed for protein immobilization. Other modifications include hydroxylation of proline and lysine, phosphorylation of hydroxyl groups of seryl or threonyl residues, methylation of the X- amino groups of lysine, arginine, and histidine side chains (T.E. Creighton, Proteins: Structure and Molecule Properties, W.H. Freeman & Co. , San Francisco, pp. 79-86 (1983)), acetylation of the N- terminal amine, and, in some instances, amidation of the C-terminal carboxy1 groups. Such derivatized moieties may improve the solubility, absorption, biological half life, and the like. The moieties may alternatively eliminate or attenuate any undesirable side effect of the protein and the like. Moieties capable of mediating such effects are disclosed, for example, in Remington's Pharmaceutical Sciences. 16th ed. , Mack Publishing Co., Easton, PA (1980) This invention is also directed to an antibody specific for an epitope of RPTPjS, preferably, of human RPTP3, and the use of such antibody to detect the presence of, or measure the quantity or concentration of, the RPTP3 in a cell, a cell or tissue extract, or a biological fluid. The term "antibody" is meant to include polyclonal antibodies, monoclonal antibodies (mAbs) , chimeric antibodies, and anti-idiotypic (anti-Id) antibodies. Polyclonal antibodies are heterogeneous populations of antibody molecules derived from the sera of animals immunized with an antigen. Monoclonal antibodies are a substantially homogeneous population of antibodies to specific antigens. MAbs may be obtained by methods known to those skilled in the art. See, for example Kohler and Milstein, Nature 256:495-497 (1975) and U.S. Patent No. 4,376,110. Such antibodies may be of any immunoglobulin class including IgG, IgM, IgE, IgA, and any subclass thereof. The hybridoma producing the mAbs of this invention may be cultivated in vitro or in vivo. Production of high titers of mAbs in vivo production makes this the presently preferred method of production. Briefly, cells from the individual hybridomas are injected intraperitoneally into pristane-primed BALB/c mice to produce ascites fluid containing high concentrations of the desired mAbs. MAbs of isotype IgM or IgG may be purified from such ascites fluids, or from culture supernatants, using column chromatography methods well known to those of skill in the art. Chimeric antibodies are molecules different portions of which are derived from different animal species, such as those having variable region derived from a murine mAb and a human immunoglobulin constant region. Chimeric antibodies and methods for their production are known in the art (Cabilly et al. Proc. Natl. Acad. Sci. USA 1:3273-3277 (1984); Morrison et al . , Proc. Natl. Acad. Sci. USA 81:6851-6855 (1984); Boulianne et al. , Nature 312:643-646 (1984); Neuberger et al. , Nature 314:268-270 (1985); Taniguchi et al. , European Patent Application 171496 (published February 19, 1985); Morrison et al. , European Patent Application 173494 (published March 5, 1986); Neuberger et al . , PCT Application WO 86/01533 (published March 13, 1986); Kudo et al . , European Patent Application 184187 (published June 11, 1986) ; Morrison et al . , European Patent Application 173494 (published March 5, 1986); Sahagan et al . , J. Immunol. 137:1066-1074 (1986); Robinson et al . , International Patent Publication #PCT/US86/02269 (published 7 May 1987); Liu et al . , Proc. Natl. Acad. Sci. USA J34:3439-3443 (1987); Sun et al . , Proc. Natl. Acad. Sci. USA 8 :214-218 (1987); Better et al . , Science 240:1041- 1043 (1988)). These references are hereby incorporated by reference. An anti-idiotypic (anti-Id) antibody is an antibody which recognizes unique determinants generally associated with the antigen-binding site of an antibody. An anti-Id antibody can be prepared by immunizing an animal of the same species and genetic type (e.g. mouse strain) as the source of the mAb with the mAb to which an anti-Id is being prepared. The immunized animal will recognize and respond to the idiotypic determinants of the immunizing antibody by producing an antibody to these idiotypic determinants (the anti-Id antibody) . The anti-Id antibody may also be used as an "immunogen" to induce an immune response in yet another animal, producing a so-called anti- anti-Id antibody. The anti-anti-Id may be epitopically identical to the original mAb which induced the anti-Id. Thus, by using antibodies to the idiotypic determinants of a mAb, it is possible to identify other hybrid clones expressing antibodies of identical specificity. Accordingly, mAbs generated against RPTP/3 may be used to induce anti-Id antibodies in suitable animals, such as BALB/c mice. Spleen cells from such immunized mice are used to produce anti-Id hybridomas secreting anti-Id mAbs. Further, the anti-Id mAbs can be coupled to a carrier such as keyhole limpet hemocyanin (KLH) and used to immunize additional BALB/c mice. Sera from these mice will contain anti-anti-Id antibodies that have the binding properties of the original mAb specific for an RPTPjS epitope. The anti-Id mAbs thus have their own idiotypic epitopes, or "idiotopes" structurally similar to the epitope being evaluated, such as an epitope of RPTP3. The term "antibody" is also meant to include both intact molecules as well as fragments thereof, such as, for example, Fab and F(ab') 2 , which are capable of binding antigen. Fab and F(ab*) 2 fragments lack the Fc fragment of intact antibody, clear more rapidly from the circulation, and may have less non-specific tissue binding than an intact antibody (Wahl et al.. J. Nucl. Med. 24:316-325 (1983)). It will be appreciated that Fab and F(ab') 2 and other fragments of the antibodies useful in the present invention may be used for the detection and quantitation of RPTP/S according to the methods disclosed herein for intact antibody molecules. . Such fragments are typically produced by proteolytic cleavage, using enzymes such as papain (to produce Fab fragments) or pepsin (to produce F(ab') 2 fragments). An antibody is said to be "capable of binding" a molecule if it is capable of specifically reacting with the molecule to thereby bind the molecule to the antibody. The term "epitope" is meant to refer to that portion of any molecule capable of being bound by an antibody which can also be recognized by that anti- body. Epitopes or "antigenic determinants" usually consist of chemically active surface groupings of molecules such as amino acids or sugar side chains and have specific three dimensional structural characteristics as well as specific charge characteristics. An "antigen" is a molecule cr a portion of a molecule capable of being bound by an antibody which is additionally capable of inducing an animal to produce antibody capable of binding to an epitope of that antigen. An antigen may have one, or more than one epitope. An antibody is said to be specific for an antigen because it reacts in a highly selective manner, with that antigen and not with the multitude of other antigens which are structurally distinct. The antibodies, or fragments of antibodies, useful in the present invention may be used to quantitatively or qualitatively detect the presence of cells which express the RPTP3 protein. This can be accomplished by immunofluorescence techniques employing a fluorescently labeled antibody (see below) coupled with light microscopic, flow cytometric, or fluorimetric detection. For such methods, the antibody is preferably specific for an extracellular epitopic of RPTP3. The antibodies (or fragments thereof) useful in the present invention may be employed histologically, as in immunofluorescence or immunoelectron microscopy, for in situ detection of RPTP. In situ detection may be accomplished by removing a histological specimen from a patient, and providing the a labeled antibody of the present invention to such a specimen. The antibody (or fragment) is preferably provided by ap¬ plying or by overlaying the labeled antibody (or fragment) to a biological sample. Through the use of such a procedure, it is possible to determine not only the presence of the RPTPjS but also its distribution on the examined tissue. Using the present invention, those of ordinary skill will readily perceive that any of a wide variety of histological methods (such as staining procedures) can be modified in order to achieve such in situ detection. Such assays for RPTP0 typically comprise incubating a biological sample, such as a biological fluid, a tissue extract, freshly harvested cells such as lymphocytes or leucocytes, or cells which have been incubated in tissue culture, in the presence of a detectably labeled antibody specific for RPTP/3, and detecting the antibody by any of a number of techniques well-known in the art. The biological sample may be treated with a solid phase support or carrier such as nitrocellulose, or other solid support which is capable of immobilizing cells, cell particles or soluble proteins. The support may then be washed with suitable buffers followed by treatment with the detectably labeled RPTP3-specific antibody. The solid phase support may then be washed with the buffer a second time to remove unbound antibody. The amount of bound label on said solid support may then be detected by conventional means. By "solid phase support" is intended any support capable of binding antigen or antibodies. Well-known supports, or carriers, include glass, polystyrene, polypropylene, polyethylene, dextran, nylon, amylases, natural and modified celluloses, polyacrylamides, gabbros, and magnetite. The nature of the carrier can be either soluble to some extent or insoluble for the purposes of the present invention. The support material may have virtually any possible structural configuration so long as the coupled molecule is capable of binding to an antigen or antibody. Thus, the support configuration may be spherical, as in a bead, or cylindrical, as in the inside surface of a test tube, or the external surface of a rod. Alternatively, the surface may be flat such as a sheet, test strip, etc. Preferred supports include polystyrene beads. Those skilled in the art will know many other suitable carriers for binding antibody or antigen, or will be able to ascertain the same by use of routine experimentation. The binding activity of a given lot of anti-RPTP/3 antibody may be determined according to well-known methods. Those skilled in the art will be able to determine operative and optimal assay conditions for each determination by employing routine experimentation. One of the ways in which the RPTP/3-specific anti¬ body can be detectably labeled is by linking the antibody, or linking a second antibody which binds to the anti-RPTP7 antibody, to an enzyme and use in an enzyme im unoassay (EIA) . This enzyme, in turn, when later exposed to an appropriate substrate, will react with the substrate in such a manner as to produce a chemical moiety which can be detected, for example, by spectrophotometric, fluorimetric or by visual means. Enzymes which can be used to detectably label the antibody include, but are not limited to, malate dehydrogenase, staphylococcal nuclease, delta-5- steroid isomerase, yeast alcohol dehydrogenase, alpha- glycerophosphate dehydrogenase, triose phosphate isomerase, horseradish peroxidase, alkaline phosphatase, asparaginase, glucose oxidase, beta- galactosidase, ribonuclease, urease, catalase, glucose-6-phosphate dehydrogenase, glucoamylase and acetylcholinesterase. The detection can be accomplished by colorimetric methods which employ a chromogenic substrate for the enzyme. Detection may also be accomplished by visual comparison of the extent of enzymatic reaction of a substrate in comparison with similarly prepared standards. Detection may be accomplished using any of a variety of other immunoassayε. For example, by radioactively labeling the antibodies or antibody fragments, it is possible to detect R-PTPase through the use of a radioimmunoassay (RIA) (see, for example, Work, T.S. et al.. Laboratory Technigues and Biochemistry in Molecular Biology, North Holland Publishing Company, New York, 1978, which is incorporated by reference herein) . The radioactive isotope can be detected by such means as the use of a gamma counter or a scintillation counter or by autoradiography. It is also possible to label the antibody with a fluorescent compound. When the fluores ently labeled antibody is exposed to light of the proper wave length, its presence can then be detected due to fluorescence. Among the most commonly used fluorescent labelling compounds are fluorescein isothiocyanate, rhodamine, phycoerythrin, phycocyanin, allophycocyanin, o- phthaldehyde and fluorescamine. The antibody can also be detectably labeled using fluorescence emitting metals such as 152 Eu, or others of the lanthanide series. These metals can be attached to the antibody using such metal chelating groups as diethylenetriaminepentaacetic acid (DTPA) or ethylenediaminetetraacetic acid (EDTA) . The antibody also can be detectably labeled by coupling it to a chemiluminescent compound. The presence of the chemiluminescent-tagged antibody is then determined by detecting the presence of luminescence that arises during the course of a chemical reaction. Examples of particularly useful chemiluminescent labeling compounds are luminol, isoluminol, theromatic acridinium ester, imidazole, acridinium salt and oxalate ester. Likewise, a bioluminescent compound may be used to label the antibody of the present invention. Bioluminescence is a type of chemiluminescence found in biological systems in which a catalytic protein increases the efficiency of the chemiluminescent reaction. The presence of a bioluminescent protein is determined by detecting the presence of luminescence. Important bioluminescent compounds for purposes of labeling are luciferin, luciferase and aequorin. The antibody molecules of the present invention may be adapted for utilization in an immunometric assay, also known as a "two-site" or "sandwich" assay. In a typical immunometric assay, a quantity of unlabeled antibody (or fragment of antibody) is bound to a solid support and a quantity of detectably labeled soluble antibody is added to permit detection and/or quantitation of the ternary complex formed between solid-phase antibody, antigen, and labeled antibody. Typical, and preferred, immunometric assays include "forward" assays in which the antibody bound to the solid phase is first contacted with the sample being tested to extract the antigen from the sample by formation of a binary solid phase antibody-antigen complex. After a suitable incubation period, the solid support is washed to remove the residue of the fluid sample, including unreacted antigen, if any, and then contacted with the solution containing an unknown quantity of labeled antibody (which functions as a "reporter molecule") . After a second incubation period to permit the labeled antibody to complex with the antigen bound to the solid support through the unlabeled antibody, the solid support is washed a second time to remove the unreacted labeled antibody. In another type of "sandwich" assay, which may also be useful with the antigens of the present invention, the so-called "simultaneous" and "reverse" assays are used. A simultaneous assay involves a single incubation step as the antibody bound to the solid support and labeled antibody are both added to the sample being tested at the same time. After the incubation is completed, the solid support is washed to remove the residue of fluid sample and uncomplexed labeled antibody. The presence of labeled antibody associated with the solid support is then determined as it would be in a conventional "forward" sandwich assay. In the "reverse" assay, stepwise addition first of a solution of labeled antibody to the fluid sample followed by the addition of unlabeled antibody bound to a solid support after a suitable incubation period is utilized. After a second incubation, the solid phase is washed in conventional fashion to free it of the residue of the sample being tested and the solution of unreacted labeled antibody. The determination of labeled antibody associated with a solid support is then determined as in the "simultaneous" and "forward" assays. The presence of normally functioning RPTP/3 in a subject can also be tested using direct enzymatic assays, for the tyrosine phosphatase activity. Such biochemical measurements can be performed in vitro, using purified enzymes, allowing precise measurements of enzyme activity, or with membrane preparations, or whole cells, where the net phosphotyrosine level is determined. In additional embodiments of the present invention, a nucleic acid molecule, preferably DNA, comprising a sequence encoding an RPTP/3 protein molecule and methods for expressing the DNA sequence are provided. One of ordinary skill in the art will know how to identify and clone additional PTPase molecules, of human or other mammalian species, which have sequence homology to the RPTP/3 molecules described herein, using the genetic sequences and oligonucleotides of the present invention without undue experimentation. Furthermore, manipulation of the genetic constructs of the present invention allow the grafting of a particular ligand-binding receptor domain onto the transmembrane and catalytic portions of the RPTP/3 resulting in chimeric molecules. Non- limiting examples of such chimeric molecules include the RPTP3 wherein the receptor is an epidermal growth factor receptor, a fibroblast growth factor receptor, n d the like. Genetically engineered chimeric recep¬ tors are known in the art (see, for example, Riedel, H. et al.. Nature 324:628-670 (1986)). Genetic constructs encoding RPTP/3, functional derivative thereof, and chimeric molecules such as those described above, can be used in gene therapy. An abnormal or dysfunctional RPTPjS, which results in disease, may be replaced by infusion of cells of the desired lineage (such as hemopoietic cells, neurons, etc.) transfected with DNA encoding normal RPTPjS. Alternatively, or additionally, cells carrying a chimeric RPTP/3 having a receptor to a ligand of choice (e.g., EGF) can be used for such gene therapy. The recombinant DNA molecules of the present invention can be produced through any of a variety of means, such as, for example, DNA or RNA synthesis, or more preferably, by application of recombinant DNA techniques. Techniques for synthesizing such molecules are disclosed by, for example, Wu, R. , et al. (Prog. Nucl. Acid. Res. Molec. Biol. 21:101-141 (1978)). Procedures for constructing recombinant molecules in accordance with the above- described method are disclosed by Sambrook et al. (supra) . Oligonucleotides representing a portion of an RPTP/3 are useful for screening for the presence of genes encoding such proteins and for the cloning of an RPTP3 gene. Techniques for synthesizing such oligonucleotides are disclosed by, for example, Wu et al . , supra) . Protein molecules are fragmented as with cyanogen bromide, or with proteases such as papain, chymotrypsin, trypsin, etc. (Oike, Y., et al.. J. Biol. Chem. 257:9751-9758 (1982); Liu, C. , et al.. Int. J. Pept. Protein Res. 2.1:209-215 (1983)). Because the genetic code is degenerate, more than one codon may be used to encode a particular amino acid (Watson, J.D., In: Molecular Biology of the Gene. 4th Ed., Benjamin/Cummings Publishing Co., Inc., Menlo Park, CA (1987)). Using the genetic code, one or more different oligonucleotides can be identified, each of which would be capable of encoding the amino acid. The probability that a particular oligonucleotide will, in fact, constitute the actual XXX-encoding sequence can be estimated by considering abnormal base pairing relationships and the frequency with which a particular codon is actually used (to encode a particular amino acid) in eukaryotic cells. Such "codon usage rules" are disclosed by Lathe, R. , et al. , J. Molec. Biol. 183:1-12 (1985). Using such "codon usage rules", a single oligonucleotide, or a set of oligonucleotides, that contains a theoretical "most probable" nucleotide sequence capable of encoding RPTP3 is identified. Although occasionally an amino acid sequence may be encoded by only a single oligonucleotide, frequently the amino acid sequence may be encoded by any of a set of similar oligonucleotides. Importantly, whereas all of the members of this set contain oligonucleotides which are capable of encoding the peptide fragment and, thus, potentially contain the same oligonucleotide sequence as the gene which encodes the peptide fragment, only one member of the set contains the nucleotide sequence that is identical to the nucleotide sequence of the gene. Because this member is present within the set, and is capable of hybridizing to DNA even in the presence of the other members of the set, it is possible to employ the unfractionated set of oligonucleotides in the same manner in which one would employ a single oligonucleotide to clone the gene that encodes the RPTP3. The oligonucleotide, or set of oligonucleotides, containing the theoretical "most probable" sequence capable of encoding the RPTP0 fragment is used to identify the sequence of a complementary oligonucleotide or set of oligonucleotides which is capable of hybridizing to the "most probable" sequence, or set of sequences. An oligonucleotide containing such a complementary sequence can be employed as a probe to identify and isolate the RPTP/3 gene (Sambrook et al.. supra) . A suitable oligonucleotide, or set of oligonucleotides, which is capable of encoding a fragment of the RPTP3 gene (or complementary to such an oligonucleotide) is identified as above and synthesized, using procedures well known in the art (Belagaje, R. , et al . , J. Biol. Chem. 254:5765-5780 (1979); Maniatis, T. , et al . , Xn: Molecular Mechanisms in the Control of Gene Expression. Nierlich, D.P., et al., Eds., Acad. Press, NY (1976); Wu, R. , et al. , Procf. Nucl. Acid Res. Molec. Biol. 21:101-141 (1978); Khorana, R.G. , Science 203:614-625 (1979)). DNA synthesis may be achieved using an automated synthesizers. The oligonucleotide probe or set is hybridized by means well known in the art, against a DNA or, more preferably, a cDNA preparation derived from cells which are capable of expressing the RPTP/3 gene. Techniques of nucleic acid hybridization are disclosed by Sambrook et al. (supra) , and by Haymes, B.D., et al. (In: Nucleic Acid Hybridization, A Practical Approach. IRL Press, Washington, DC (1985)), which references are herein incorporated by reference. Techniques such as, or similar to, those described above have successfully enabled the cloning of genes for human aldehyde dehydrogenases (Hsu, L.C, et al.. Proc. Natl. Acad. Sci. USA 82:3771-3775 (1985)), fibronectin (Suzuki, S., et al.. EMBO J. 4.:2519-2524 (1985)), the human estrogen receptor gene (Walter, P., et al. , Proc. Natl. Acad. Sci. USA 8_2:7889-7893 (1985)), tissue-type plasminogen activator (Pennica, D., et al.. Nature 301:214-221 (1983)) and human term placental alkaline phosphatase complementary DNA (Kam, W. , et al. , Proc. Natl. Acad. Sci. USA 82: (715-8719 (1985)). In a alternative way of cloning the RPTP/3 gene, a library of expression vectors is prepared by cloning DNA or, more preferably, cDNA (from a cell capable of expressing RPTP / 3) into an expression vector. The library is then screened for members capable of expressing a protein which binds to anti-RPTP3 antibody, and which has a nucleotide sequence that is capable of encoding a polypeptide that has the same amino acid sequence as all or part of RPTP3. In this embodiment, DNA, or more preferably cDNA, is extracted and purified from a cell which is capable of expressing RPTP0 protein. The purified cDNA is fragmented (by shearing, endonuclease digestion, etc.) to produce a pool of DNA or cDNA fragments. DNA or cDNA fragments from this pool are then cloned into an expression vector in order to produce a genomic library of expression vectors whose members each contain a unique cloned DNA or cDNA fragment. An "expression vector" is a vector which (due to the presence of appropriate transcriptional and/or translational control sequences) is capable of expressing a DNA molecule which has been cloned into the vector and of thereby producing a peptide or protein. Expression of the cloned sequences occurs when the expression vector is introduced into an appropriate host cell. If a prokaryotic expression vector is employed, then the appropriate host cell would be any prokaryotic cell capable of expressing the cloned sequences. If a eukaryotic expression vector is employed, then the appropriate host cell would be any eukaryotic cell capable of expressing the cloned sequences. Importantly, since eukaryotic DNA may contain intervening sequences, and since such sequences cannot be correctly processed in prokaryotic cells, it is preferable to employ cDNA from a cell which is capable of expressing RPTPγ in order to produce a prokaryotic genomic expression vector library. Procedures for preparing cDNA and for producing a genomic library are disclosed by Sambrook et al. (supra) . A DNA sequence encoding the RPTP3 of the present invention, or its functional derivatives, may be recombined with vector DNA in accordance with conventional techniques, including blunt-ended or staggered-ended termini for ligation, restriction enzyme digestion to provide appropriate termini, filling in of cohesive ends as appropriate, alkaline phosphatase treatment to avoid undesirable joining, and ligation with appropriate ligases. Techniques for such manipulations are disclosed by Sambrook et al . , supra, and are well known in the art. A nucleic acid molecule, such as DNA, is said to be "capable of expressing" a polypeptide if it contains nucleotide sequences which contain transcriptional and translational regulatory information and such sequences are "operably linked" to a polypeptide coding sequence. An operable linkage is a linkage in which the regulatory DNA sequences and coding sequence are connected in such a way as to permit gene expression. The precise nature of the regulatory regions needed for gene expression may vary from organism to organism, but shall in general include a promoter region which, in prokaryotes, contains both the promoter (which directs the initia¬ tion of RNA transcription) as well as the DNA sequences which, when transcribed into RNA, will signal the initiation of protein synthesis. Such regions will normally include those 5'-non-coding sequences involved with initiation of transcription and translation, such as the TATA box, capping sequence, CAAT sequence, and the like. If desired, the non-coding region 3* to the coding sequence may be obtained by the above-described methods. This region may be retained for its transcriptional termination regulatory sequences, such as termination and polyadenylation. Thus, by retaining the 3'-region naturally contiguous to the DNA coding sequence, the transcriptional termination signals may be provided. Where the transcriptional termination signals are not satisfactorily functional in the desired host cell, then a 3* region functional in the host cell may be substituted. Two DNA sequences (such as a promoter region sequence and a RPTP/3 coding sequence) are said to be operably linked if the nature of the linkage between the two DNA sequences does not (1) result in the introduction of a frame-shift mutation, (2) interfere with the ability of the promoter to regulate direct the transcription of the RPTPjS coding sequence. A promoter region is operably linked to a DNA coding sequence if the promoter is capable of effecting transcription of the coding sequence. Thus, to express the protein, transcriptional and translational signals recognized by an appropriate host are necessary. In order to be "operably linked" it is not necessary that two sequences be immediately adjacent to one another. A promoter is a double-stranded DNA (or RNA) molecule which is capable of binding to RNA polymerase and promoting the transcription of an "operably linked" nucleic acid coding sequence. As used herein, a "promoter sequence" is the sequence of the promoter which is found on that strand of the DNA (or RNA) which is transcribed by the RNA polymerase. A "promoter sequence complement" has a sequence which is the complement of the "promoter sequence." Hence, upon extension of a primer DNA or RNA adjacent to a single-stranded "promoter sequence complement" or, of a "promoter sequence," a double-stranded molecule is created which will contain a functional promoter, if that extension proceeds towards the "promoter sequence" or the "promoter sequence complement." This functional promoter will direct the transcription of a nucleic acid molecule which is operably linked to that strand of the double-stranded molecule which contains the "promoter sequence" (and not that strand of the molecule which contains the "promoter sequence complement") . Certain RNA polymerases exhibit a high specificity for such promoters. The RNA polymerases of the bacteriophages T7, T3, and SP-6 are especially well characterized, and exhibit high promoter specificity. The promoter sequences which are specific for each of these RNA polymerases also direct the polymerase to transcribe from only one strand of a duplex DNA template. Strand selection is determined by the orientation of the promoter sequence, and determines the direction of transcription since RNA is only polymerized enzymatically by the addition of a nucleotide 5' phosphate to a 3' hydroxyl terminus. The promoter sequences of the present invention may be either prokaryotic, eukaryotic or viral. Suitable promoters are repressible, or, more preferably, constitutive. Examples of suitable prokaryotic promoters include promoters capable of recognizing the T4 (Malik, S. et al.. J. Biol. Chem. 2j53_:1174-1181 (1984); Rosenberg, A.H. et al.. Gene 59:191-200 (1987); Shinedling, S. et al.. J. Molec. Biol. 195:471-480 (1987).; Hu, M. et al.. Gene 42:21-30 (1986)), T3, Sp6, and T7 (Chamberlin, M. et al.. Nature 228:227-231 (1970); Bailey, J.N. et al. , Proc. Natl. Acad. Sci. CU.S.A.^ 80:2814-2818 (1983); Davanloo, P. et a1.. Proc. Natl. Acad. Sci. (U.S.A.') 8.1:2035-2039 (1984)) polymerases; the P R and P L promoters of bacteriophage λ (The Bacteriophaqe Lambda, Hershey, A.D., Ed., Cold Spring Harbor Press, Cold Spring Harbor, NY (1973); Lambda II, Hendrix, R.W. , Ed., Cold Spring Harbor Press, Cold Spring Harbor, NY (1980)); the trp, recA, heat shock, and lacZ promoters of E. coli; the α-amylase (Ulmanen, I., et al.. J. Bacteriol. 162 : 176-182 (1985)) and the σ- 28-specific promoters of B. subtilis (Gil an, M.Z., et al.. Gene 3_2.:ll-20 (1984)) ; the promoters of the bacteriophages of Bacillus (Gryczan, T.J. , In: The Molecular Biology of the Bacilli. Academic Press, Inc., NY (1982)); Strepto yces promoters (Ward, J.M. , et al.. Mol. Gen. Genet. 203:468-478 (1986)); the int promoter of bacteriophage λ; the bla promoter of the β-lactamase gene of pBR322, and the CAT promoter of the chloramphenicol acetyl transferase gene of pPR325, etc. Prokaryotic promoters are reviewed by Glick, B.R. (J . Ind. Microbiol. 1:277-282 (1987)); Cenatiempo, Y. (Biochimie 68:505-516 (1986)); Watson, J.D. et al. (In: Molecular Biology of the Gene. Fourth Edition, Benjamin Cummins, Menlo Park, CA (1987)); and Gottesman, S. (Ann. Rev. Genet. JL8_:415-442 (1984)). Preferred eukaryotic promoters include the promoter of the mouse metallothionein I gene (Hamer, D. , et al.. J. Mol. APPI. Gen. 1:273-288 (1982)); the TK promoter of Herpes virus (McKnight, S., Cell 31:355-365 (1982)); the SV40 early promoter (Benoist, C, et al.. Nature fLondon. 290:304-310 (1981)); and the yeast gal4 gene promoter (Johnston, S.A., et al.. Proc. Natl. Acad. Sci. (USA) 79:6971-6975 (1982); Silver, P. ., et al.. Proc. Natl. Acad. Sci. fUSA. 81:5951- 5955 (1984)). All of the above listed references are incorporated by reference herein. Strong promoters are preferred. Examples of such preferred promoters are those which recognize the T3, SP6 and T7 polymerases, the P L promoter of bacteriophage λ, the recA promoter and the promoter of the mouse metallothionein I gene. A most preferred promoter for eukaryotic expression of RPTP is an SV40 promoter such as that driving transcription in the pLSV vector (Livneh, E. , et al.. (1986) J. Biol. Chem. 261, 12490- 12497) . The sequences of such polymerase recognition sites are disclosed by Watson, J.D. et al. (In: Molecular Biology of the Gene. Fourth Edition, Benjamin/Cummings Publishing Co., Inc., Menlo Park, CA, (1987)). Having now generally described the invention, the same will be more readily understood through reference to the following example which is provided by way of illustration, and is not intended to be limiting of the present invention, unless specified. 6. EXAMPLE: ISOLATION AND CHARACTERIZATION OF HUMAN RPTPθ cDNA 6.1. MATERIALS Restriction endonucleases and modifying enzymes were purchases from Boehringer-Mannheim or New England Biolabs. Taq DNA polymerase was from Perkin- Elmer/Cetus. The λgtll forward and reverse primers (24-mers) used in the polymerase chain reactions as well as all sequencing primers, were synthesized on an automated DNA synthesizer (Applied Biosystems, model 380A) using either methoxy or β-cyanoethyl phosphoramidites (House, C, et al.. J. Biol. Chem.. 262:772-777 (1987)). The λgtll human brainstem cDNA library was obtained form the American Type Culture Collection (no. 37432) . The LCA (CD45) clone used as a probe for screening the library was received from E.H. Fischer (University of Washington, Seattle) . All sequencing reactions were performed using the Sequenase kit (United States Biochemical) . 6 . 2 . METHODS A cDNA clone containing a portion of the coding sequences for RPTP3 was isolated after screening a λgtll human infant brain stem cDNA library under conditions of reduced stringency with a nick translated LCA probe that included both phosphatase domains (Kaplan et al . , Proc. Natl . Acad. Sci . USA 87:7000-7004 (1990)). Since the 5' end of this gene was not present in the original clone, the library was rescreened with a DNA fragment that was generated from the 5'end of the original clone. The probe was labeled with 32 P-dCTP utilizing the random prime method (USB) and hybridization was performed under moderately stringent conditions at 42°C in a buffer containing 50% formamide, 5XSSC, 20mM Tris-HCl pH 7.6, IX Denhardt's solution, 0.1% SDS and 100 μg/ml of sheared and denatured salmon sperm DNA. After hybridization, o phage filters were washed three times for 20 min at 50°C in a buffer containing O.lXSSC/0.1% SDS and then were processed for autoradiography. The brainstem library was rescreened a total of three times in order to isolate overlapping cDNA clones that contained the 5 entire coding sequence for RPTPβ. cDNA inserts from positive recombinant plaque- purified phage were subcloned into the plasmid vector, BlueScript (Stratagene, La Jolla, CA) , and sεquenced by the dideoxy chain termination method using the 0 Sequenase Version 2.0 Kit (USB). 6.3. RESULTS The present inventors previously isolated a 5 portion of a novel RPTP denoted RPTPjS (co-pending commonly assigned U.S. Patent Application Serial No. 07/654,188, filed February 26, 1991, from which the present application claims priority; Kaplan et al. , 1990, supra) . A similar phosphatase was independently cloned by another group and was termed called PTP$ * (Krueger et al. , 1990, supra ; Krueger et al . , 1992, supra) . The reasons for the sequence differences between RPTP/3 disclosed herein and PTPf are not yet clear. Four overlapping cDNA clones containing the entire coding sequence for RPTP/3 were isolated from a human brain stem library. The deduced amino acid sequence reveals an open reading frame of 2307 amino acids (Figure 2) . RPTP3 belongs to the high molecular weight, transmembrane class of PTPases. The sequence contains a signal peptide (underlined in Figure 2) followed by a long extracellular domain of 1611 amino acids containing 21 potential N-glycosylation sites (indicated by arrows in Figure 2) . A hydrophobic, transmembrane peptide (bold sequences in Figure 2) joins the extracellular portion of the protein to two tandemly repeated and conserved phosphatase domains (designated DI and DII) . One distinguishing feature of this phosphatase is the homology it shares with different isoforms of carbonic anhydrase (CAH) over a stretch of 283 amino acids located at the extreme amino terminus of the protein (designated CAH in Figure 2) . In addition to RPTP3, the extracellular domain of a related RPTP, RPTPγ, shares homology with CAH (co-pending commonly assigned U.S. Patent Application Serial No. 07/654,188, filed February 26, 1991, from which the present application claims priority; co-pending commonly assigned U.S. Patent Application Serial No. , filed May 10, 1993, titled " Novel Receptor-Type Phosphotyrosine Phosphatase-Gamma) . Alignment of the CAH-related domains of RPTPjS and RPTP7 with the six known isoforms of CAH is shown in Figure 3A. Figure 3B shows the percent similarity, taking into account conservative amino acid substitutions, between the CAH-related domain of RPTP3, the corresponding domain of RPTP/3 and the six CAH enzymes. The amino acid sequence similarity of the CAH-related domain of RPTP/3 to the six CAH isoforms ranges from 45-50%. The highest degree of similarity (58%) exists between the CAH-related sequences of RPTP and RPTP7. Therefore, RPTPjS and RPTP7 represent a new subgroup of RPTPs characterized by the presence of CAH-related regions in the amino terminal portions of their extracellular domains. 7. EXAMPLE: CHROMOSOMAL LOCALIZATION OF THE HUMAN RPTP/3 GENE 7.1. METHODS Isolation, propagation and characterization of parental and somatic cell hybrids used in this study have been described (Durst et al . , Proc . Natl . Acad . Sci . USA 84:1070-1074 (1987); Huebner et al . , Am . J. Hum . Genet . 48:726-740 (1991)). Presence of specific human chromosomes or regions of chromosomes has been confirmed by DNA hybridization using probes for genes assigned to specific chromosome regions. Figure 4A depicts diagrammatically the chromosomes or partial chromosomes retained in most of the hybrids used. Chromosomal in situ hybridization was performed as described (Cannizzarro et al., Cancer Res . 51:3818- 3820 (1991)). Slides containing metaphase chromosomes from normal male (46 XY) peripheral blood lymphocytes were aged at 4°C for 7-10 days and pretreated with ribonuclease A (Sigma) for 1 h at 37°C. The chromosomal DNA was denatured in a hybridization mixture containing 50% formamide, 2X SSC and 10% dextran sulfate (pH 7.0) . Hybridization was carried out at 37°C overnight. After rinsing at 39°C in three changes of 50% formamide and 2X SSC, and five changes of 2X SSC, slides were dehydrated, air dried, subjected to autoradiography and banded with Wright's- Giemsa stain solution mixed with 1-3 parts of ph 9.2 borate buffer (Cannizzaro et al . , supra) . 7.2. RESULTS The chromosomal localization of the human RPTP/3 gene was initially determined utilizing a panel of rodent-human hybrids carrying defined human chromosomes or chromosome regions. The results from screening the rodent-human hybrids which are summarized in Figure 4A, correlates the presence of the human RPTPj3 locus in hybrid cells with human chromosome 7. A more precise localization of the RPTPjSf gene was determined by chromosomal in situ hybridization to metaphase chromosomes of normal human lymphocytes. This technique places the RPTP gene at 7q31-33 with the most likely position at 7q31.3-q32 which is diagrammatically shown to the right of the chromosome sketch in Figure 4B. 8. EXAMPLE: EXPRESSION OF RPTP RNA 0 8.1. ISOLATION OF MOUSE SEQUENCES HOMOLOGOUS TO HUMAN RPTPβ Two oligonucleotides in conserved phosphatase domain II were synthesized according to the nucleotide sequence of human RPTPβ. These oligonucleotides in ^ conjunction with phage DNA from a mouse brain cDNA library (Clonetech, Palo Alto, CA) were used in the PCR with Taq polymerase (Perkin-Elmer) to amplify homologous mouse RPTPβ sequences. The amplified product was purified and cloned into the BlueScript plasmid vector (Stratagene, La Jolla, CA) . Homology was confirmed by DNA sequence analysis as described above. This subcloned fragment is called pBSMBDII. 8.2. NORTHERN ANALYSIS Total cellular RNA was prepared with the Stratagene RNA isolation kit. Poly A 4* RNA was further selected utilizing oligo-dT cellulose chromatography (Stratagene) . For Northern analysis, the RNA was separated on a 1.0% agarose/2.2 M formaldehyde gel and transferred to a Nytran membrane (Schleicher and Schuell) by capillary action. The membrane was prehybridized and hybridized in 0.5 M sodium phosphate ph 7.2, 7% SDS, 1 mM EDTA, 100 μg/ml salmon sperm DNA and then washed in 40 mM sodium phosphate ph 7.2, 1% SDS, 1 mM EDTA at 65°C. For the blot containing RNA isolated from various mouse tissues, a 32 P-labeled probe was made utilizing PBSMBDII as template in the random primer labeling reaction (US Biochemicals) . The human glioblastoma and neuroblastoma RNA blots were probed with labeled restriction fragments isolated from different parts of the human RPTP/3 cDNA clones. 8.3. ANTIBODIES A peptide derived from the carboxy-terminal 15 amino acids of human RPTPjS was synthesized and coupled to keyhole limpet hemocyanin according to standard procedures. Two rabbits were inoculated to produce polyclonal antisera against RPTP7. Anti-EGF receptor immunoprecipitates were performed with RK2 antibody which recognizes the EGF receptor (Kris et al . , Cell 40:619-625 (1985)). 8.4. CELL LABELING AND IMMUNOPRECIPITATION The human neuroblastoma cell line, Lan 5, was maintained in Dulbecco's modified Eagle's medium (DMEM) containing 10% fetal bovine serum (FBS) . Cultured cells were incubated with 10 μg/ml tunicamycin (Sigma Chemical Co.) for 1 hour prior to [ 35 S]-methionine labeling. Treated and untreated cells were washed twice with methionine free DMEM and labeled for 4 hours with 0.15 mCi/ml [ 35 S]-methionine (NEN, DuPont) in DMEM lacking methionine and supplemented with 1% dialyzed FBS. During the labeling period, 10 μg/ml tunicamycin was added to the medium of the treated cells. Cells were then washed with ice cold phosphate buffered saline (PBS) and solubilized in a lysis buffer containing 50 mM N-2- hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES, pH 7.5), 150 mM NaCl, 1.0% Triton X-100, 10% glycerol, 1.5 mM MgCl 2 , 1 mM ethylene glycol-bis [B— aminoethyl ether]-N,N,N' ,N'-tetraacetic acid (EGTA), 10 μg of leupeptin per ml, 1 mM phenylmethylsulfonyl fluoride, and 10 μg of aprotinin per ml. Cell lysates were clarified and then immunoprecipitated with normal rabbit serum, rabbit anti-RPTP/3 antiserum or RK2 antiserum for 2 hour at 4°C. The immune complexes were precipitated with Protein A-Sepharose (Sigma Chemical Co.) for 45 min at 4°C and washed 10 times with RIPA buffer (20mM Tris-HCl, pH 7.6,- 300 mM NaCl, 2 mM EDTA, 1.0% Triton X-100, 1.0% sodium deoxycholate and 0.1% SDS). The immunoprecipitated material was analyzed on a 7.5% SDS-polyacrylamide gel and fluorography. 8.5. RESULTS: DETECTION OF RPTPjS EXPRESSION IN A HUMAN NEUROBLASTOMA CELL LINE. Lan 5 Since all of the clones encoding the entire sequence for RPTPβ were isolated from a human brain stem library, the expression of RPTP/3 mRNA was examined in different human glioblastoma cell lines and a human neuroblastoma cell line, Lan 5 (Sonnenfield et al . , J . Neurosci . Res . 8:375-391 (1982)) . A human RPTPβ probe hybridized to three major transcripts of 8.8, 7.5 and 6.4 kb, respectively (Figure 5A) . These transcripts were only detected in RNA isolated from the Lan 5 neuroblastoma cell line and were absent in the RNA isolated from the four glioblastoma cell lines even though similar amounts of total cellular RNA were loaded as revealed by ethidiu-m bromide staining of the 28S and 18S ribosomal RNAs. In order to obtain further insights into the nature of the three RPTP/3 transcripts, performed an additional Northern analysis was performed on RNA isolated from Lan 5 cells with probes derived from nonconserved sequences in the extracellular domain of RPTP3. An identical pattern of transcripts was revealed utilizing these probes. The Lan 5 neuroblastoma cell line was used to study the endogenous expression of RPTPjS protein. Cell lysates prepared from cultures labeled with [ 35 S]methionine for 4 hours were immunoprecipitated with normal rabbit serum or anti-RPTPjS antiserum (Figure 6) . A protein with apparent molecular weight of approximately 300 kDa was recognized by the anti- RPTP/3 antiserum but not by normal rabbit serum (lanes 1 and 2) . Since there are 21 potential N- glycosylation sites, tunicamycin was employed to examine the possibility that the 300 kDa protein immunoprecipitated by the anti-RPTP/3 antiserum was a glycosylated form of RPTPjS. The effects of tunicamycin treatment on the mobility of RPTP/3 immunoprecipitated from [ 35 S]methionine-labeled cells was compared to its ability to inhibit the glycosylation of the EGF receptor which is also expressed in this cell line. Untreated cell lysates and lysates prepared from cells treated with tunicamycin were immunoprecipitated with an anti EGF receptor antibody (RK2) that recognizes the 170 kDa glycosylated and the 135 kDa nonglycosylated forms of the EGF receptor (Kris et al . , supra) . These results are also shown in Figure 6, lanes 4 and 5). The protein immunoprecipitated with anti-RPTP/3 antiserum from Lan 5 cells that had been metabolically labeled in the presence of tunicamycin (Figure 6, lane 3) migrated with an apparent molecular weight of 250 kDa. This result was consistent with the predicted molecular weight of 254 kDa deduced from the amino acid sequence of RPTP / 3. 9. EXAMPLE: IDENTIFICATION OF A VARIANT FORM OF RPTPβ The overlapping human cDNA clones collectively contained approximately 8.1 kb of coding and noncoding sequences and appeared to represent the largest transcript that is 8.8 kb in length. In screening the human brain stem library and a human caudate library (Stratagene, La Jolla, CA) , the present inventors isolated two independent cDNA clones that each contained an identical deletion of 2577 nucleotides from the extracellular domain of RPTPj3. This in-frame deletion joined amino acid 754 to amino acid 1614 (shown by the open arrows in Figure 2 and in Figure 7A) thereby maintaining the transmembrane domain and the two phosphatase domains. A deletion of this size could account for the difference between the 8.8 kb and 6.4 kb transcripts expressed in the Lan 5 neuroblastoma cell line (Figure 5A) . Hence, duplicate blots were made from RNA isolated from the Lan 5 cell line. One blot was analyzed with a probe that should hybridize to both the full length and deleted forms of RPTP7 (Pl) . The other blot was analyzed with a probe that should only hybridized to the full length form (P2) . The location of probes 1 and 2 in the full length RPTP)3 cDNA is shown in Figure 7A. Northern analysis with the two probes shown in Figure 7B revealed that probe 1 hybridized to the three distinct transcripts (Pl) whereas probe 2 hybridized only to the 7.5 and 8.8 kb transcripts (P2) . This result suggested that the 6.4 kb transcript represented a deleted variant form of RPTP/S which could be the result of alternative mRNA splicing. However, only the high molecular weight form of RPTP/3 was detected following immunoprecipitation with anti RPTP/3 antibodies and SDS-PAGE analysis (Figure 6) . The reason for the inability to detect the low molecular weight form in lysates from of RPTP3 in Lan5 cells is not clear. 10. EXAMPLE: TISSUE SPECIFIC EXPRESSION OF RPTPβ 10.1. METHODS: IN SITU HYBRIDIZATION ANALYSIS Fresh frozen tissue was cut on a cryostat into 20 μm thick sections and thaw mounted onto gelatin coated slides. The sections were fixed in 4% paraformaldehyde in 0.1 M sodium phosphate (pH 7.4) for 30 min and rinsed three time for 5 min each in 0. 1 M sodium phosphate and once for 10 min in 2X SSC. Two probes were used in the hybridization analysis; (1) a 49 base oligonucleotide complementary to phosphatase domain II, and (2) a 50 base oligonucleotide complementary to the carbonic anhydrase-like domain. The oligonucleotides was labeled with [ (α- 35 S]dATP (NEN, DuPont) using terminal deoxynucleotidyl transferase (Boehringer Mannheim) and purified using Sephadex G25 quick spin columns (Boehringer Mannheim) . The specific activity of the labeled probes was between 5 x 10 8 and 1 x 10 9 cpm/μg. Prehybridizations and hybridizations were carried out in a buffer containing 50% deionized formamide, 4X SSC, IX Denhardt's, 500 μg/ml denatured salmon sperm DNA, 250 μg/ml yeast tRNA and 10% dextran sulfate. The tissue was incubated for 12 h at 45°C in hybridization solution containing the labeled probe (1 x 10 6 cpm/section) and 10 mM dithiothreitol (DTT) . Controls for specificity were performed on adjacent sections by diluting the labeled oligonucleotides with a 30-fold concentration of the appropriate unlabeled oligonucleotide and by hybridization with a sense probe. After hybridization, the sections were washed in 2 changes of 2X SSC at room temperature for 1 h, IX SSC at 55°C for 30 min, 0.5X SSC at 55°C for 30 min, 0.5X SSC at room temperature for 15 min and dehydrated in 60%, 80%, and 100% ethanol. After air drying, the sections were exposed to X-ray film for 5-10 d. 10.2. RESULTS 10.2.1. Tissue Specific Expression of RPTPJ3 Northern analysis of various tissue RNAs was performed to determine the tissue-specific expression of RPTPjS. The probe used in this analysis was a portion of the murine homolog of RPTP/3 that was amplified in the PCR (described above) and contains 405 nucleotides encoding 135 amino acids of Domain II. Based on a nucleotide sequence comparison to the equivalent region of the human cDNA clone, the murine and human clones are 88% identical at the nucleotide level in this region of Domain II of RPTP3. The results of this Northern analysis (Figure 5B) indicated the presence of two major transcripts of 8.8 and 6.4 kb, respectively. These two transcripts are similar in size to the largest and smallest transcripts observed in Lan 5 RNA (see Figure 5A) . However, no band corresponding to the 7.5 kb transcript was detected. A minor transcript of approximately 9.4 kb was sometimes observed in RNA prepared from mouse brain tissue and may represent cross-reaction to a highly related phosphatase. RPTP3 transcripts were not detected in the lung, heart, liver, spleen, kidney, muscle, testes and thymus. The quality of the RNA isolated from the various tissues was compared by parallel hybridization with an actin probe of the same blots (Figure 5C) . Hence, Northern hybridization analysis indicates that RPTPβ mRNA is strictly expressed in the brain of the adult mouse. 10.2.2. Localization of RPTPj3 Expression in the Brain In order to more precisely localize the expression of RPTP/3 in the brain, in situ hybridization was performed on brain tissue from the adult and the embryonic mouse. The results of this analysis confirmed that RPTP/3 was expressed in the central nervous system. In a day 20 embryonic mouse (E20) , a high level of expression was observed in the ventricular and subventricular zones of the brain (Figure 8A) , and in the spinal cord. The level of expression was lower in the adult brain, and was localized to the Purkinje cell layer of the cerebellum, the dentate gyrus, and the subependymal layer of the anterior horn of lateral ventricle (Figure 8B) . Both probes (complementary to the CAH-like domain and the second phosphatase domain) gave identical results. The addition of a 30-fold excess of unlabeled oligonucleotide completely blocked the labeling in all areas. Furthermore, no signal was observed in adjacent sections hybridized with the sense probe, indicating that the probes hybridize to mRNA in a sequence specific manner. These results demonstrated that RPTPjS has a restricted tissue specificity to specific regions of the nervous system. 11. GENERAL DISCUSSION FOR SECTIONS 6-10 The present inventor has cloned and characterized a human RPTP that is expressed in the central nervous system and cannot be detected in other murine tissues. Amino acid sequence analysis revealed that RPTP3 has a striking degree of sequence homology at it N-terminal end with various isoforms of the enzyme CAH over a stretch of 283 amino acids. RPTP7 was also found to contain a CAH-related sequence near the amino terminus in the extracellular domain. Therefore, RPTP/3 and RPTP7 are concluded to be members of a new subgroup of transmembrane phosphatases that can be classified on the basis of a CAH-related domain present in the amino terminal regions of their extracellular domain. A three dimensional model of the CAH-related domain of RPTP7 based upon the known crystal structure of CAH and a detailed description of this model was provided elsewhere by the present inventors laboratory (see, for example, co-pending commonly assigned U.S. Patent Application Serial No. , filed May 10, 1993, titled "Novel Receptor-Type Phosphotyrosine Phosphatase-Gamma) . Since key residues known to participate in the catalytic activity of CAH are missing from both RPTP/3 (as well as from RPTP7) , it is likely that the CAH domains in these two phosphatases do not possess classical carbonic anhydrase activity. It has been postulated that under-expression or inactivation of PTPases might lead to oncogenesis suggesting that PTPases may function as tumor suppressors. This finds support in the findings from the present inventor's laboratory that RPTP7 maps to human chromosome region 3p21, a region is frequently deleted in both renal cell and lung carcinomas (LaForgia et al . , supra) . The presently reported localization of the human RPTP/3 gene to human chromosome 7q31.3-q32 renders it important to investigate loss of, or mutations in, the RPTPjS gene in certain tumor types, especially those exhibiting deletions of 7q. In the case of the PTPase termed CD45, alternative mRNA splicing was shown to produce six distinct isoforms, as a result of the differential usage of three exons encoding sequences in the extracellular domain (Streuli et al . , J . Exp . Med . 166:1548-1566 (1987); Streuli et al. , EMBO J. 8:787- 796 (1989)). Alternative splicing within the first catalytic domain of RPTPα has also been described (Matthews et al . , Proc . Natl . Acad . Sci . USA 87:4444- 4448 (1990)). The results of Northern blot analysis reveal the presence of multiple RPTP/3 transcripts in both mouse brain and a human neuroblastoma cell line, Lan 5, that appear to either result from alternatively spliced transcripts or from highly related genes. The Northern blot analyses indicate that the 8.8 kb and the 6.4 kb transcripts are strictly expressed in the brain. Northern blot analysis described in Figure 5 in conjunction with the analysis of two independently isolated cDNA clones suggest that the smallest transcript of 6.4 kb may result from a deletion of approximately 2.6 kb encoding a large portion of the extracellular domain of RPTP3. τ he importance of tyrosine phosphorylation in the control and regulation of specific neuronal processes is under intense investigation. It was demonstrated that tyrosine phosphorylation is enhanced at the time of synaptogenesis during development (Cudmore et al . , J. Neuroche-m. 57:1240-1248 (1991); Girault et al . , Proc . Natl . Acad . Sci . USA 89:2769-2773 (1992); Qu et al . , Neuron 2:367-378 (1990)) and may play a role in synaptic plasticity in the adult (Girault et al., J. Neurochem. 58:518-528 (1992)). In addition, NGF and other neurotrophic factors mediate their effects on neuronal survival by binding to and activating receptors with tyrosine kinase activity (Cordon-Cardo et al . , Cell 66:1-20 (1991); Kaplan et al . , Science 252:554-557 (1991); Klein et al . , Cell 65:189-197 (1991); Schlessinger, J. et al. , Neuron 9:383-391 (1992) . Stimulation of other growth factor receptors with tyrosine kinase activities have profound effects on survival and differentiation of cultured neurons (Aizen an et al . , Brain Res . 406:32-42 (1987); Morrison et al . , Science 238 : 72-75 (1987)) suggesting a potential role in normal neuronal development. Finally, several cytoplasmic tyrosine kinases including the products of the proto-oncogenes c-src and c-yes are expressed at high levels in specific regions of neurons of the adult brain (Pang et al., Proc . Natl . Acad . Sci . USA 85:762-7661988a; Pang et al . , Soc . Neurosci . Abstr. 14:44.6 (1988); Maness et al . , Proc . Natl . Acad . Sci . USA 85:5001-5005 (1988); Sudol et al . , Molec . Cell . Biol . 9:4545-4549 (1989)). RPTP/3 represents the first cloned mammalian PTPase whose tissue specific expression is restricted to the nervous system. Several Drosophila RPTPs have been identified that are selectively expressed on central nervous system axons in the embryo (Tian et al . , Cell 67:675-685 (1991); Yang et al . , Cell 67:661- 673 1991) . The identification of brain-specific PTPases, such as RPTP/3, is an important initial step towards understanding the regulation of tyrosine phosphorylation by the PTPases in mammalian neural tissues. The relatively high level of RPTP/3 expression in the embryonic central nervous system CNS suggests that it plays a role in the development of the nervous system. It is of note that the ventricular and subventricular zones are the primary sites of cell division in the developing brain (Altman et al . , Exp. Neurol . 107:23-35 (1990). Interestingly, RPTP/3 is expressed in the few regions of the adult brain that continue to show itotic activity such as the dentate gyrus and the subependymal layer of the anterior horn of the lateral ventricle. Immunocytochemical techniques are being applied to determine the precise cellular distribution of RPTP/3 protein and to help elucidate its role in the regulation of specific developmental and neuronal processes. The sequences of the conserved phosphatase domains of the human RPTP/3, as described in detail above, is compared in Table I, below, with RPTPα and RPTP7 and with the sequences of LCA, LAR, and two soluble PTPases, placental phosphatase IB and T-cell PTPase. The two soluble enzymes have a sequence identity of 70%; however, when each is compared with the RPTPs (Phosphatase domains PDI or PD2, also referred to above as PDI and PDII) , this number drops to 29-42%. In all cases, the soluble PTPases showed a greater identity with PDI than with PD2 of the RPTPs. RPTPα appears to be most related to LAR, since their PDI sequences are 56% identical and their PD2 sequences are 52% identical. The conserved domains of RPTPβ and RPTP7 are most related to each other, even more so than are the two soluble PTPases, β and 7 being 75% identical in both PDI and PD2. It is interesting that, in general, the sequence relationship between PDI and PD2 within any RPTP appears to be no closer than that seen between different members of the family, i.e., the identities between PDI and PD2 range from a high of 47% for LAR to a low of 29% for RPTP 7. While the cytoplasmic domains of RPTPα, β, and 7 are highly conserved, the extracellular domains of these receptors are unrelated to one another as well as to those of LAR and LCA. This suggests that each of these receptors has its own distinct ligand. It is likely that the binding of such ligands to the RPTPs plays a crucial role, together with growth factor receptors exhibiting PTKase activity, in the regulation of the level of tyrosine phosphorylation of targets proteins involved in signal transduction. The diversity of the RPTPs described herein reveals the existence of a multigene family. Greater understanding of structure-function relationships among these membrane receptors will provide important insights into the mechanisms involved in cell growth, differentiation, and oncogenesis. Although the inventor does not intend to be bound by any particular theory, the high interspecies conservation of the catalytic domains of the various RPTPs indicates an important role for these receptors in cell growth control. Table 4 Identities Between Conserved Phosphatase Domains (Percent) PTPase T-cell LCA AR RPTPase-α RPTPase-β RPTPase-7 IB PTPase PDI PDI PDI PD2 PDI PD2 PDI PD2 PDI PD2 PTPase IB 100 T-cell PTPase 70 100 10 LCA PDI 37 36 100 LCA PD2 30 26 31 100 LAR PDI 39 42 50 28 100 LAR PD2 29 33 42 34 45 100 R-PTPase-α PDI 36 38 50 32 56 45 100 R-PTPase-α PD2 33 34 40 32 41 52 43 100 R-PTPase-β PDI 35 39 41 31 33 41 47 33 100 R-PTPase-β PD2 29 30 31 30 31 34 31 37 30 100 15 R-PTPase-7 PDI 35 34 32 29 39 36 34 32 75 27 100 R-PTPase-7 PD2 29 29 30 28 32 36 31 34 33 75 29 100 Alignments of the conserved phosphatase domains were carried out as described above. The regions compared are designated in Figure 4C and Figure 5. PD=phosphatase domain. 20 25 The references cited above are all incorporated by reference herein, whether specifically incorporated or not. Having now fully described this invention, it will be appreciated by those skilled in the art that the same can be performed within a wide range of equivalent parameters, concentrations, and conditions without departing from the spirit and scope of the invention and without undue experimentation. While this invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications. This application is intended to cover any variations, uses, or adaptations of the inventions following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth as follows in the scope of the appended claims.

Claims: WHAT IS CLAIMED IS; 1. A human receptor-type protein tyrosine phosphatase-/3 protein or glycoprotein molecule, a functional derivative thereof, or a homolog thereof in other mammals, wherein, when said molecule is one which naturally occurs, said molecule is substantially free of other proteins or glycoproteins with which it is natively associated. 2. A molecule according to claim 1, which does not occur in nature. 3. A molecule according to claim 1, which occurs in nature and is substantially free of other proteins or glycoproteins with which it is associated in natively associated. 4. A molecule according to claim 1 having the amino acid sequence SEQ ID NO:l, or a functional derivative thereof. 5. A nucleic acid molecule encoding a receptor- type protein tyrosine phosphatase-jS protein according to claim 1, or encoding a functional derivative thereof, wherein, when said protein or functional derivative is one which naturally occurs, said nucleic acid molecule is substantially free of nucleotide sequences encoding proteins with which said protein or functional derivative is natively associated. 6. A nucleic acid molecule according to claim 5 which is a cDNA molecule. 7. A nucleic acid molecule according to claim 5 which is a genomic DNA molecule. 8. A nucleic acid molecule according to claim 5 which is a DNA molecule, having the nucleotide sequence SEQ ID:NO. 2. 9. A nucleic acid molecule according to claim 5 which is an expression vehicle. 10. The nucleic acid molecule of claim 9 wherein said expression vehicle is a plasmid. 11. A prokaryotic host transformed with the plasmid of claim 10. 12. A eukaryotic host transformed or transfected with an expression vehicle according to claim 9. 13. A process for preparing a receptor-type protein tyrosine phosphatase-j3 protein or glycoprotein according to claim 1, or a functional derivative thereof, said process comprising: (a) culturing a host capable of expressing said protein, glycoprotein or functional derivative under culturing conditions, (b) expressing said protein, glycoprotein or functional derivative; and (c) recovering said protein, glycoprotein or functional derivative from said culture. 14. A process according to claim 13 wherein said host is a prokaryote. 15. A process according to claim 13 wherein said host is a eukaryote. 16. An antibody specific for the protein or glycoprotein of claim 1. 17. An antibody according to claim 16 which is monoclonal. 18. A method for detecting the presence of a nucleic acid molecule according to claim 5, or a mutant thereof, in a subject, comprising: (a) contacting a cell or an extract thereof from said subject with an oligonucleotide probe encoding at least a portion of said normal or said mutant receptor-type protein tyrosine phosphatase-jS under hybridizing conditions; and (b) measuring the hybridization of said probe to the nucleic acid of said cell, thereby detecting the presence of said nucleic acid sequence. 19. The method of claim 18, additionally comprising before step (a) : (c) selectively amplifying the amount of DNA of said cell encoding said receptor-type protein tyrosine phosphatase-jS. 20. A method for detecting in a cell the presence or measuring the quantity of a receptor-type protein tyrosine phosphatase-/3 protein or glycoprotein, comprising: (a) contacting said cell or an extract thereof with an antibody according to claim 16; and (b) detecting the binding of said antibody to said cell or extract thereof, or measuring the quantity of antibody bound, thereby determining the presence or measuring the quantity of said receptor-type protein tyrosine phosphatase-/3 protein or glycoprotein. 21. A method for identifying in a chemical or biological preparation a compound capable of binding to a receptor-type protein tyrosine phosphatase-jS protein, glycoprotein or derivative according to claim 1, said method comprising: (a) attaching said receptor-type protein tyrosine phosphatase-3 protein, glycoprotein or derivative, or the ligand-binding portion thereof to a solid phase matrix; (b) contacting said chemical or biological preparation with said solid phase matrix allowing said compound to bind, and washing away any unbound material; and (c) detecting the presence of said compound bound to said solid phase. 22. A method for isolating from a complex mixture a compound capable of binding to a receptor- type protein tyrosine phosphatase-/3 protein, glycoprotein or functional derivative according to claim l, comprising: (a) attaching said receptor-type protein tyrosine phosphatase-/3 protein, glycoprotein or functional derivative, or the ligand- binding portion thereof, to a solid phase matrix; 94/18308 - 69 - (b) contacting said complex mixture with said solid phase matrix allowing said compound to bind, and washing away any unbound material; and (c) eluting said bound compound, thereby isolating said compound. 23. A method for identifying an agent capable of stimulating or inhibiting the enzymatic activity of a receptor-type protein tyrosine phosphatase-/-?, comprising: (a) contacting said agent with said receptor- type protein tyrosine phosphatase-jS in pure form, in a membrane preparation, or in a whole cell; (b) incubating said mixture of step (a) for a sufficient interval; (c) measuring the enzymatic activity of said receptor-type protein tyrosine phosphatase- β; (d) comparing said enzymatic activity to that of said receptor-type protein tyrosine phosphatase-j3 incubated without said agent, thereby determining whether said agent stimulates or inhibits said activity.

Inventors: SCHLESSINGER JOSEPH, SCHLESSINGER, JOSEPH
Applicants: UNIV NEW YORK, NEW YORK UNIVERSITY
Application year: 1994
Main classification: C12N1
IPC codes: A61K38, A61K39, A61K45, A61P43, C07K14, C07K16, C12N1, C12N5, C12N9, C12N15, C12P21, C12Q1, C12R1, G01N33